It is old to utilize centering devices to stabilize an internal pipe cutter, and to employ the cutter for internal parting of a pipe, especially downhole in a borehole. There seldom is any need to internally cut pipe that is located above the ground merely to part the pipe into shorter joints because it is far easier to cut the pipe externally.
Applicant has discovered that it is possible to mount a special shaft driven cutter device onto a mandrel, support the cutter device fore and aft within a pipe, thereby axially aligning the center of the cutter device respective to the longitudinal central axis of the pipe, and to remove a small interior part of the pipe surface with precision to provide the pipe with a uniform inside diameter in a manner somewhat similar to cutting the inner surface of a cylinder on a lathe, for example. However, it is difficult to properly support a cutting device internally of long joints or sections of large, heavy pipe and to accurately remove the inner surface of the pipe in order that the entire inner wall surface of the pipe is rendered of constant diameter.
In the oil field heavy, expensive, long, large outside diameter pipe, called casing, is cemented into position along the entire length of the borehole of an oil well. Thus, the pipe is used for casing a borehole. For example, ten inch casing having a wall thickness approaching one-half inch is used downhole in boreholes having a depth of twenty thousand feet, for example. The casing is expensive and can represent more than one half million dollars, not counting the expense of installing the casing in the wellbore. For this and other reasons, the drilling companies will not run casing into the borehole until it has been "drifted"; that is, a selected size metal cylinder must freely slide through each section or joint of the pipe, whereupon the pipe sections are then pronounced as being drifted; that is, it has an acceptable or proper inside diameter. Often irregularities randomly occur on the inside wall surface of pipe sections that preclude the pipe from being acceptable for use in deep wells and this is referred as "undrifted pipe" or pipe that is too small to accept the drift. This undrifted pipe is perfectly good except that it cannot be used downhole in the borehole because the oil company must be assured that the entire borehole is of a minimum diameter, so that there is no subsequent danger of sticking a tool string, or other devices, downhole in the borehole.
Applicant has discovered that the undrifted pipe can be reclaimed economically by running a cutter head made in accordance with his invention through the undrifted pipe. The cutterhead, together with a considerable amount of support equipment, provides a method of drifting pipe so that the expensive undrifted casing can be reclaimed and properly employed as drifted casing.
Included in the discovery is a novel grinder device for reworking pipe having marginal imperfections.